1. Field of the Invention
The present invention relates generally to an optical recording (writing) and reproducing (reading or playing back) apparatus for forming pits on an optical recording medium depending on given data to be recorded using a light spot projected from a recording light projection optical system. The present invention includes a semiconductor laser to record the data on the optical recording medium. The optical recording medium is illuminated using a light spot projected from a reproducing light projection optical system. The reflected light from the optical recording medium is converted into an electrical signal through a reproducing light reception optical system including a light receiving element to read data represented by the pits. More particularly the present invention involves a recording and reproducing apparatus for a WORM storage medium (write once, read many) forming new pits to record additional data in an unrecorded region subsequent to the recorded pits on the optical recording medium. 2. Description of the Prior Art
The format shown in FIG. 1a represents a known format (continuous WORM type format) for recording data in pit form on a track of a card-shaped optical recording medium used in this type of optical recording and reproducing apparatus.
In the continuous WORM type format shown in FIG. 1a, one track of an optical recording medium includes a plurality of sectors A, B, C and D. The sectors A to D are contiguous to each other. The sectors A to D respectively comprise data portions a.sub.1 to d.sub.1 in which data are recorded and sector information portions a.sub.2 to d.sub.2 in which information regarding the sectors are recorded. A lead portion e.sub.2 is the track information portion. In the continuous WORM type format, no space indicating the boundary between the contiguous sectors exists between the sectors. For example, as shown in FIG. 1b, the first pit P.sub.bs out of pits P.sub.b in the succeeding sector B is additionally recorded (additionally formed) subsequently to the last pit P.sub.ae out of pits P.sub.a recorded (formed) in the preceding sector A.
In order to properly establish synchronization in continuously reproducing the pits in the sectors A and B, when data is additionaly recorded in the sector B subsequently to the sector A, the first pit P.sub.bs in the sector B must be recorded in a position which is synchronous with the position of the last pit P.sub.ae in the sector A. The sector information portion a.sub.2 exists in the rear end of the sector A, as described above. Pits indicating a mark or pattern representing the end of the sector (referred to as sector end pattern hereinafter) are formed in this sector information portion a.sub.2. The recording and reproducing apparatus must comprise a means for properly reading such a sector end pattern and forming the first pit P.sub.bs to be recorded in the sector B in a position which is properly synchronous with the position of the last pit P.sub.ae in the sector A.